The aim of this study is to investigate the differences in brain activation in healthy subjects during motor tasks, depending on the laterality of the subject, the laterality of the task and the complexity of the task. It seems that the laterality of activation is less marked in left-handed people, when using the non-dominant hand and when performing a complex task. The objective of this study is to highlight profiles of subject and modality of use of the hand with a specific lateralization of cerebral activation.

Stroke frequently leads to upper limb deficit. The recovery of motor skills depends on many factors including laterality. The literature shows that cerebral activation during motor tasks differs depending on whether one is right-handed or left-handed and whether one uses the dominant hand or not. These differences probably lead to different recovery mechanisms depending on the side of the lesion and the laterality. An imaging technique is particularly suitable for exploring these different mechanisms: fNIRS (Functional Near Infra Red Spectroscopy). This method allows (like fMRI) to study cerebral neurovascular coupling. It is based on the fact that an activated brain region increases its local blood flow. Oxygenated (HbO) and deoxygenated (HbR) hemoglobin absorb infrared light and it is then possible to identify the cerebral cortical regions involved in a given task. This technique therefore makes it possible to study cerebral activation under more ecological conditions than fMRI and is thus particularly suitable for exploring rehabilitation techniques.

This research aims to study and compare in healthy subjects, using an fNIRS apparatus, the brain regions involved in the performance of different motor tasks according to the laterality of the task and the subject.

The investigations will be carried out by the principal investigator or by specialized technicians from the neurology functional exploration department.

Stroke frequently leads to upper limb deficit. The recovery of motor skills depends on many factors including laterality. The literature shows that cerebral activation during motor tasks differs depending on whether one is right-handed or left-handed and whether one uses the dominant hand or not. These differences probably lead to different recovery mechanisms depending on the side of the lesion and the laterality. An imaging technique is particularly suitable for exploring these different mechanisms: fNIRS (Functional Near Infra Red Spectroscopy). This method allows (like fMRI) to study cerebral neurovascular coupling. It is based on the fact that an activated brain region increases its local blood flow. Oxygenated (HbO) and deoxygenated (HbR) hemoglobin absorb infrared light and it is then possible to identify the cerebral cortical regions involved in a given task. This technique therefore makes it possible to study cerebral activation under more ecological conditions than fMRI and is thus particularly suitable for exploring rehabilitation techniques.

This research aims to study and compare in healthy subjects, using an fNIRS apparatus, the brain regions involved in the performance of different motor tasks according to the laterality of the task and the subject.

The investigations will be carried out by the principal investigator or by specialized technicians from the neurology functional exploration department.

The acquisition has a duration of 25 minutes, it begins with a rest period of 120 seconds, which corresponds to the baseline. Four different tasks are performed during the acquisition for each subject:

• Simple task right hand (SD)
• Simple task left hand (SG)
• Complex task right hand (CD)
• Complex stain left hand (CG)

The design is a block design, each task, which has a duration of 20 seconds, is carried out 8 times per acquisition. There is therefore a total of 32 tasks whose order will be randomized.

For simple tasks, movements are performed at a frequency of 0.5 Hz which appears to be the optimal frequency for observing cortical activation using a metronome.

Between periods of movement, the subject is in a rest position for a period from 15 to 25 seconds.

Instructions are given verbally at the start of each phase. After recruiting the subjects, the study investigator will check the inclusion and exclusion criteria.

If the subject can integrate the protocol, the acquisition will then be planned.

On the day of the acquisition, the fNIRS acquisition helmet (Brite MKII) will be installed by a specialist technician and instructions will be given. The recording is then made.

Inclusion Criteria:

• Subject from 18 to 60 years old
• Sufficient command of the French language to understand the instructions
• No known neurological medical history
• Benefiting from social security coverage
• For right-handed subjects: Edinburgh laterality test QL> 40
• For left-handed subjects: Edinburgh laterality test QL< -40

Exclusion Criteria:

• Known allergy to components of the fNIRS device : neoprene